The protozoan parasite Trypanosoma brucei subspecies are the causative agent of African sleeping sickness, a disease that is invariably fatal without treatment. T. brucei has served as a model system for the study of the related trypanosomatid pathogens Trypanosoma cruzi and Leishmania spp., and the three together infect over 12 million people worldwide. The absence of vaccines and the toxic nature of drugs that combat sleeping sickness make research into new drug targets imperative. With the release of the genome sequences of these three trypanosomatids, there are now important decisions as to which of many candidate targets to pursue. Protein kinases are a large class of enzymes that serve as drug targets in cancer and other diseases. They sense the extracellular or intracellular environment and regulate numerous cellular responses, including cell division, responses to stress, development, and death. This project proposes the use of conditional knockout and chemical genetic approaches to examine the roles of protein kinases likely to play a role in host-parasite interactions. We have prioritized two novel protein kinases that reside in T. brucei membranes at the flagellum and flagellar pocket. This region of the parasite plays a prominent role in cell motility and division, nutrient acquisition, and immune evasion mechanisms. Surprisingly, unlike other eukaryotic protein kinases, these kinases possess multiple membrane spanning domains, implying novel modes of information coupling. Our RNAi studies indicate that they are important in the pathogenic bloodstream stage and their location within the parasite predicts a significant role in host-parasite interactions. Conditional knockous of the kinases will firmly establish the role of the kinases in vitro and in a mouse model. A chemical genetic approach using mutant forms of the kinases will be pursued to determine whether specific drug inhibition causes the same phenotypes as absence of the protein, conclusively assessing the suitability of these protein kinases as drug targets and providing the opportunity to dissect the pathways in which the kinases function.